I have the Sigma 24-70mm F2.8 EX DG Macro and it is a fine lens. I also have the 70-200mm F4L which, IMO, is stellar. If most of your shooting is in daylight, the F4 lenses will work fine for you. FWIW, the 24-70mm Sigma is very slow to focus, at least compared to my Canon 70-200mm F4L and is relatively noisy while focusing. Of course, with outside shooting, the noise will probably not be an issue. Also, my Sigma 24-70mm had to go back to Sigma for a front focusing issue that seems to be common with that lens. So, if you go that route, do not be surprised if it has to go back for the "flexboard" upgrade.
Don't get me wrong, I like my Sigma 24-70mm. In fact, I probably use it more than the 70-200mm F4L due to the focal length. Just thought you should know the whole story. If it were me, shooting outside, I would go with 70-200mm F4L and 17-40mm F4L. Shooting outside in daylight, you will probably never use F2.8.
Canon EOS 7D with BG-E7 battery grip, EOS 40D with BG-E2 battery grip, Canon 20D, Canon EF 70-200mm F2.8L IS, Canon EF 24-70mm F2.8[COLOR=#ff0000]L, EF 300mm F4L IS, EF 400mm F5.6L, EF-S 17-40mm F4.0L, Canon Speedlite 580EX